Use a web proxy

Docker Trusted Registry makes outgoing connections to check for new versions,
automatically renew its license, and update its vulnerability database.
If DTR can’t access the internet, then you need to manually apply updates.

One option to keep your environment secure while still allowing DTR access to
the internet is to use a web proxy. If you have an HTTP or HTTPS proxy, you
can configure DTR to use it. To avoid downtime you should do this configuration
outside business peak hours.